Such seed drill elements are designed to be mounted either individually or as a group on a chassis, itself pulled by an agricultural tractor.
The invention applies in particular to sowing seeds one at a time, in particular for cultivating maize (corn), beet, and sunflowers, whose seeds need to be put into the ground individually, and they need to be spaced apart with predetermined spacing.
One of the important parameters for good sowing is the depth at which seeds are buried in the ground, i.e. the distance between the surface of the ground and the seed. In agriculture, this depth at which the seed is buried can be referred to as the “topsoiling” (or covering) depth. In addition, there are three different topsoiling techniques depending on whether the weight of the seed drill element is supported mainly in front of the furrow-opening zone, mainly behind said zone, or both in front and behind said zone by means of a rocker structure.
For this purpose, modern seed drill elements are thus provided with topsoiling means designed to implement each topsoiling technique and to impose a substantially constant depth of furrow depending on the nature, the firmness, and the surface irregularities of the ground being sown.
At present, some such topsoiling means are in the form of a micrometer screw which causes the arm holding the front or rear wheel to move towards or away from the frame of the element so as to decrease or increase the difference in height between the bottom face of the furrow-opening member and the level of the front or rear wheel pressed against the ground. This can be referred as topsoiling depth being set by the front or the rear wheel(s).
When topsoiling depth is determined by a rocker, i.e. by co-operation between a front block and a rear block, the means for setting topsoiling depth often comprise a handle for adjusting the length of the intermediate link in such a manner as to adjust the difference in height between the front wheel(s) and the rear wheel(s) so as to set the height of the furrow-opening coulter, thereby adjusting the depth to which the furrow-opening member penetrates into the ground.
All of those means for adjusting topsoiling depth are lengthy to adjust and difficult to reproduce from one seed drill element to another, which means that it is not possible to guarantee uniform topsoiling for a group of seed drill elements all mounted on the same drive chassis.